GB/T 35974.4-2018Plastics and plastic lining pressure vessels—Part 4: Fabrication, inspection and testing for plastic pressure vessels (English PDF)

3.1 General Requirements

3.1.1 Plastics vessels shall be fabricated in accordance with the processing procedure stipulated in this Part.

3.2.2 Acceptance check

3.2.2.1 Items

Acceptance check items of materials are: quality certificate, appearance, dimensions and performance indexes.

3.2.2.2 Quality certificate

Materials shall have an exit-factory quality certificate. Items and indexes in the quality certificate shall comply with the stipulations in GB/T 35974.2.

3.2.2.3 Appearance

Materials' appearance shall receive full inspection. The indexes shall comply with the stipulations in GB/T 35974.2.

3.2.2.4 Dimensions

Materials' main dimensions shall receive 100% inspection. The indexes shall comply with the stipulations in GB/T 35974.2.

3.2.2.5 Performance indexes

Main materials' performance indexes shall comply with the stipulations in GB/T 35974.2.

3.2.3 Material re-inspection

3.2.3.1 Under one of the following circumstances, materials' performance indexes shall be re-inspected in accordance with GB/T 35974.2 and design requirements:

a) When there are doubts about the performance indexes in the quality certificate;

b) When re-inspection is requested in design documents.

3.2.3.2 Material re-inspection shall receive sampling inspection of the performance indexes. The sampling range shall cover every exit-factory batch of the materials.

Sampling inspection items shall at least include the content in Table 2. Materials shall be qualified in all the inspection items, then, they may be used in the fabrication of plastics vessels. […]

3.3.2.1.3 Cooling

Cool down the mold that is already heated. During the cooling process, the mold shall maintain the rotatory state. One of the following cooling modes, or a combination of several cooling modes may be adopted for cooling: natural cooling, water mist cooling or water spray cooling. During the cooling process, the difference between the air temperature in the mold and the external surface temperature of the mold is requested not to exceed 40 °C. When the external surface temperature of the shell decreases to 50 °C ~ 80 °C, stop the rotation of the shell.

3.3.2.1.4 Demolding and post-processing

After the cooling is completed, disassemble the plastics vessel. Adopt vibration method to eliminate the internal stress of the plastics vessel.

3.3.2.2 Procedure evaluation

Procedure evaluation shall at least include the items listed in Table 1. The various item indexes shall comply with the designed value and the stipulations in GB/T 35974.2.

3.3.3 Extrusion

3.3.3.1 Methods

3.3.3.1.1 Plasticization

Extrusion plasticization shall adopt the following methods:

a) Dry extrusion: through in-cylinder heating and heat generation by mechanical screw's rotary shearing, plastics that enter the extruder's cylinder would reach the plastics melt temperature. In accordance with the differences of materials, determine corresponding procedure parameters, such as plasticization temperature and shear torque force.

b) Wet extrusion: adopt an organic solvent to soften and dissolve plastics. In accordance with the solvent's technical parameters, determine procedure parameters, such as the matching ratio and plasticization time.

3.3.3.1.2 Molding

In accordance with plastics vessel's shape and dimensions, design a molding mold.

Under mechanical pressure, plasticized plastics enter the mold, fill up the mold cavity.

3.3.3.1.3 Cooling

Adopt the following methods for cooling, so that after cooling, the plastics vessel would reach relatively stable structure and dimensions:

a) Dry extrusion: adopt one of the following cooling modes, or a combination of several cooling modes: natural cooling, water mist cooling or water spray cooling;

b) Wet extrusion: adopt cooling modes like natural curing and heating curing.

3.3.3.1.4 Demolding and post-processing

When plastics vessel's structure and dimensions become relatively stable in the mold, disassemble the mold; take out the plastics vessel. In addition, cut off or remove redundant edges.

3.3.3.2 Procedure evaluation

Procedure evaluation shall at least include the items listed in Table 1. The various item indexes shall comply with the designed value and the stipulations in GB/T 35974.2.

3.3.4 Extrusion winding

3.3.4.1 Methods

Extrusion winding molding shall be conducted in accordance with the following three procedures:

a) Cylinder's extrusion winding molding: select the specifications of mold; determine the number of winding layers and the length of cylinder. After the cooling, demold it; make the head flat. It is requested that there shall be no gap among the layers. The minimum wall thickness shall be not less than the nominal thickness.

b) Bottom cover (head) installation: hemispherical, ellipsoidal and conical head may adopt integral injection molding or plate thermo-compression molding. In the thermo-compression of the head flap plate and top plate butt joint, welded joints are merely allowed to be in radial and circumferential direction. In accordance with the drawings, properly handle the grooves of the cylinder's joints; adopt extrusion welding equipment for welding.

c) Accessory installation: in the welding of connecting pipe's Flange and cylinder body, in accordance with the size of the connecting pipe, select an appropriate welding mode. Flange bolt holes shall be symmetrically distributed on both sides of the cylinder's axis and in mid-span distribution. When there are any special requirements, they shall be indicated in the drawings.

5.2.4 Determination

5.2.4.1 Determination of exit-factory inspection

When the result of exit-factory inspection complies with the requirements, products shall be determined as qualified. If products fail to comply with one or more requirements, they shall be determined as disqualified. Disqualified products may be returned for re-fabrication. One re-fabrication is allowed on welded joints. Two re-fabrications are allowed on other parts. After the re-fabrication, products shall be re-inspected. If products are still disqualified in the re-inspection, they shall be determined as disqualified. If there is re-fabrication, the time, the parts and the situation of the re-fabrication shall be recorded in the quality certificate.

5.2.4.2 Determination of type inspection

When the result of type inspection complies with the requirements stipulated in Table 5, products shall be determined as qualified in type inspection. If products fail to comply with one or more requirements, they shall be determined as disqualified in type inspection.

6.1 Exit-factory Information

6.1.1 Fabrication organizations shall provide exit-factory information to vessels' purchaser. When there are special requirements towards the usage of vessels, they shall also provide an instruction manual.

6.1.2 Exit-factory information shall at least include the following content:

a) Vessels' original design drawings and general completion drawings;

b) Vessels' documentary quality certificates (including product certificate, product data sheet and quality certificate);

c) Vessels' characteristics (including design pressure, maximum allowable operating pressure, test pressure, design temperature and operating medium);

d) Vessels' instruction manual.

6.2 Vessel Nameplate